1. Field of the Invention
The present invention relates in general to a board duplexing apparatus for an asynchronous transfer mode (ATM) switch and a method of controlling the same, and more particularly to a technique for individually duplexing all boards in an ATM switch, associated with a subscriber module, to increase a system efficiency.
2. Description of the Related Art
As well known to those skilled in the art, an ATM switch is a communication system that switches signals on a number of subscriber lines at high speed. The ATM switch, however, has a disadvantage in that it cannot process signals from a number of subscribers at the same time if a fault occurs in a circuit board or line for signal processing.
In order to solve the above problem with the ATM switch, there is a need for a duplexing technique to dually install circuit boards and lines in the ATM switch with duplicate boards and lines. Unfortunately, this duplexing may result in an increase in cost and a reduction in efficiency. In this regard, there is another need for a duplexing scheme capable of attaining the maximum efficiency at the minimum cost.
FIG. 1 is a functional block diagram of a conventional board duplexing apparatus for an ATM switch. As shown in this drawing, the conventional board duplexing apparatus comprises a subscriber module 10 for accommodating a plurality of subscribers to the ATM switch, and a synchronous digital hierarchy (SDH) interface card (SIC) 11 matching-connected to the subscriber module 10 through an optical line (interval A) for receiving an SDH frame from the subscriber module 10 at its ingress, extracting a plurality of cells from the received SDH frame and outputting the extracted cells at its egress. The SIC 11 is also adapted to receive a plurality of cells at its egress, convert the received cells into an SDH frame and transfer the converted SDH frame to the subscriber module 10 at its ingress.
The conventional board duplexing apparatus further comprises first and second ATM port management cards (APMCs) 12 and 13, each of which is matching connected to the SIC 11 through a Utopian data bus (interval B) to send and receive cells to/from the SIC 11. Each of the first and second APMCs 12 and 13 receives a plurality of cells from the SIC 11 at its ingress, detects or looks up headers of the received cells, appends routing tags respectively to the detected or looked-up headers, stacks the resulting cells in its internal buffer and then outputs the stacked cells at its egress according to scheduling. Each of the first and second APMCs 12 and 13 further receives a plurality of cells at its egress, performs a traffic shaping operation with respect to headers of the received cells such that the cells are appropriate to a data transfer rate of the Utopian data bus, and then transfers the resulting cells to the SIC 11 at its ingress.
The conventional board duplexing apparatus further comprises first and second switches 14 and 15, each of which is connected to the first and second APMCs 12 and 13 through serial links (interval C). Each of the first and second switches 14 and 15 receives a plurality of cells with routing tags from the first or second APMC 12 or 13 at its ingress and routes the received cells at its egress. Each of the first and second switches 14 and 15 also receives a plurality of cells at its egress and outputs the received cells to the first or second APMC 12 or 13 at its ingress.
A description will hereinafter be given of the operation of the conventional board duplexing apparatus with the above-mentioned construction with reference to FIG. 1.
In the normal initial state of the ATM switch as shown in FIG. 1, the first APMC 12 and first switch 14 are set to an active mode, whereas the second APMC 13 and second switch 15 are set to a standby mode.
The second APMC 13 of the standby mode is inhibited from making a connection to a Utopian data bus 2 under a bus switch control, while only the first APMC 12 of the active mode is connected to a Utopian data bus 1 under a bus switch control and in turn to the SIC 11 so as to send and receive cells to/from the SIC 11.
Further, the first APMC 12 sends cells to both the first switch 14 and second switch 15, but receives and switches cells from only the first switch 14 of the active mode.
In other words, cells from a connection, to be sent to a destination, are applied to and stored in both the first APMC 12 of the active mode and the second APMC 13 of the standby mode.
If a fault occurs in the first APMC 12, the first APMC 12 is disconnected from the Utopian data bus 1 by a bus switch operation under a buffer control so as to enter the standby mode, and the second APMC 13 is connected to the Utopian data bus or bus master 2 by a bus switch operation so as to enter the active mode. As a result, the second APMC 13 is connected to the SIC 11 to send and receive cells to/from the SIC 11.
Further, the second APMC 13 sends cells to both the first switch 14 and second switch 15, but receives and switches cells from only the first switch 14 of the active mode.
At this time, if a fault occurs in the first switch 14, the second switch 15 receives and switches cells from the second APMC 13.
The above-mentioned conventional board duplexing apparatus for the ATM switch is desirable to increase reliability of the system, but disadvantageous in that the same function blocks for duplexing are kept unused in the standby mode, resulting in a reduction in efficiency and an increase in opportunity cost.